Scanning Laser Projector

ABSTRACT

A scanning projector for projecting an image comprising multiple wavelength signals is disclosed. Embodiments of the present invention include a beam combiner comprising a planar lightwave circuit having a plurality of surface waveguides arranged to define a plurality of input ports, a mixing region, and an output port. Each input port receives a different wavelength signal and provides it to the mixing region. The mixing region combines the plurality of wavelength signals into a single composite output beam that is scanned over a region to create an image in a region. 
     In some embodiments, the projector (1) interrogates image points in the region using a first wavelength signal to determine a measurand and (2) projects an image over the image points of the region using a second wavelength signal, wherein each image point is illuminated with the second wavelength signal based on a measurand at that image point.

CROSS REFERENCE TO RELATED APPLICATIONS

This case is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 13/208,806 (Applicant Docket: 142-018us), entitled“Beam Combiner,” filed Aug. 12, 2011, which claims the benefit ofEuropean Patent Application EP10008424.3, filed Aug. 12, 2010, U.S.Provisional Application Ser. No. 61/344,553, filed Aug. 19, 2010(Attorney Docket: 094111-0388630), U.S. Provisional Application Ser. No.61/376,483, filed Aug. 24, 2010 (Attorney Docket: 094111-0388719), andU.S. Provisional Application Ser. No. 61/477,960, filed Apr. 21, 2011(Attorney Docket: 142-017PROV). All of these cases are incorporatedherein by reference

If there are any contradictions or inconsistencies in language betweenthis application and one or more of the cases that have beenincorporated by reference that might affect the interpretation of theclaims in this case, the claims in this case should be interpreted to beconsistent with the language in this case.

FIELD OF THE INVENTION

The present invention relates to projectors in general, and, moreparticularly, to multi-wavelength laser projectors.

BACKGROUND OF THE INVENTION

The popularity of mobile digital devices, such as smart phones, personaldata assistants, digital cameras, etc., has increased dramatically inrecent years. As a result, a typical device user routinely carries vastamounts of digital information in their pockets. In addition, access tothe Internet is rapidly becoming ubiquitous, increasing the amount ofinformation at a user's fingertips dramatically. Much of thisinformation is in the form of media, such as web pages, videos, livetelevision, photographs, books, and the like, which is meant fordisplay. Unfortunately, the small form-factor of many mobile digitaldevices, while enabling easy mobility, does not lend itself well to thedisplay of the stored information. As a result, portable projectors(often referred to as “pico-projectors”) that attach to the mobiledevices and project the information onto a convenient surface havebecome increasingly attractive. Pico-projectors have found use in manyapplications, including heads-up displays in cars and planes, businesspresentations, and entertainment.

One popular type of projector is based on the projection of laser light.Such projectors are enabled, in part, by the development of miniaturesolid-state lasers. In order to project color images, light signals frommultiple lasers (typically emitting red, green, and blue light) arecombined using free-space optics to form a composite light beam that isthen scanned over the intended display region. Unfortunately, widespreadadoption of such projectors remains slow due to their relatively largesize.

Another available projector type is based on liquid crystals (LC's).LC-based projectors either project an image through a liquid-crystaldisplay, or construct the image by reflection onto aliquid-crystal-on-silicon (LCoS) display using light bulbs or LEDs aslight sources.

Unfortunately, currently available pico-projectors are still relativelylarge, complex, and expensive. Further, projectors based on free-spaceoptical systems require labor-intensive assembly. As a result, it isdifficult to manufacture such projectors in high volume at low cost.

SUMMARY OF THE INVENTION

The present invention enables a compact laser-beam projector thatovercomes some of the costs and disadvantages of the prior art.Embodiments of the present invention are particularly well suited foruse in applications such as entertainment, medical diagnostics, cancertreatment, insect control, thermal hot spot mapping for integratedcircuits or printed-circuit boards, and virtual keyboards.

The present invention provides a platform for combining a plurality oflight signals of different wavelengths into a single output beam thatcan be scanned to render an image on a surface. Embodiments of thepresent invention are based on planar lightwave circuit-based beamcombiners that can combine a plurality of light signals of disparatewavelengths over a wide wavelength range. The beam combiner comprisesplanar lightwave circuit having a plurality of input ports, a mixingregion, and an output port, wherein the mixing region includes aplurality of directional couplers that are arranged in a tree structure.The planar lightwave circuits are based on single-mode surfacewaveguides having a core comprising stoichiometric silicon nitride andcladding of stoichiometric silicon dioxide.

Beam combiners in accordance with the present invention enable low-cost,automated assembly, hybrid integration of the beam combiners and lightsources that provide the constituent light signals. Embodiments of thepresent invention, therefore, can be less expensive and/or smaller thanlaser projectors of the prior art. Further, planar lightwavecircuit-based beam combiners can be more robust and less sensitive toshock and vibration than free-space beam combiners, resulting in laserprojectors that are more robust than typical prior-art laser projectors.

In some embodiments, at least one input port has a mode-matching regionthat enables direct, low-loss optical coupling of the output facet of alaser diode to the beam combiner. The mode-matching region includes awaveguide region that is tapered from an end facet to an interface sothat the effective refractive-index contrast at the end facet is loweror higher than the effective refractive-index contrast at the interface.At the interface, the optical mode is mode-matched to the waveguidestructure that forms the bulk of the planar lightwave circuit.

In some embodiments, the beam combiner comprises waveguide-basedattenuators for controlling the intensity one or more of the lightsignals combined in the composite output signal.

In some embodiments, reflected light from each image point in the imageregion is used to determine one or more measurands of that image point.At least one light signal in the output beam is selected so that themeasurand induces a detectable difference in its reflected light. Insome embodiments, when a difference in the reflected light is detected,one or more additional light signals of different wavelengths are addedto the output beam and are simultaneously projected onto the surface.

An embodiment of the present invention is a projector for forming areal-time image of the vein structure in a region of a patient's body onthe surface of the skin. The illustrative embodiment comprises a firstlight source that emits a light signal of a first wavelength that isreadily absorbed by the blood carried in the veins. This light signal iscollimated to form an output beam that is scanned over a region of theskin, which reflects a portion of the output beam to a photodetector.When an image point comprises a portion of a vein, the intensity of thereflected light decreases, thereby indicating the presence of the vein.In response to a decrease in the reflected signal, the projector adds asecond light signal of a second wavelength to the output beam, whereinthe second wavelength is readily visible to a user—thereby enhancingvisibility of that image point to the user. The projector scans theentire region at a rate sufficient to generate a real-time image of thesub-surface vein structure on the skin.

An embodiment of the present invention is a scanning projectorcomprising: a first light source that provides a first light signalcharacterized by a first wavelength; a second light source that providesa second light signal characterized by a second wavelength; a beamcombiner comprising a planar lightwave circuit including a plurality ofwaveguides that are arranged to define a first input port, a secondinput port, a mixing region, and an output port, the beam combiner: (1)receiving the first light signal at the first input port, (2) receivingthe second light signal at the second input port, (3) combining thefirst light signal and the second light signal into a composite outputsignal, and (4) providing the composite output signal at the outputport; and a scanner, the scanner receiving the composite output signalfrom the beam combiner and scanning the composite output signal overeach of a plurality of image points in a first region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a schematic drawing of a scanning laser projector inaccordance with the prior art.

FIG. 2 depicts a schematic drawing of a scanning projector in accordancewith an illustrative embodiment of the present invention.

FIG. 3 depicts operations of a method for projecting an image inaccordance with the illustrative embodiment of the present invention.

FIG. 4A depicts a schematic drawing of a cross-sectional view of awaveguide in accordance with the illustrative embodiment of the presentinvention.

FIG. 4B depicts a schematic drawing of a cross-sectional view of awaveguide in accordance with a first alternative embodiment of thepresent invention.

FIG. 5A depicts a schematic drawing of a top view of an input portcomprising a mode-matching region in accordance with the illustrativeembodiment of the present invention.

FIG. 5B depicts a schematic drawing of a cross-sectional view of endfacet 504-i.

FIG. 5C depicts a schematic drawing of a cross-sectional view ofinterface 506-i.

FIG. 6 depicts a schematic drawing of mixing region 214.

FIG. 7 depicts a schematic drawing of a power controller in accordancewith the illustrative embodiment of the present invention.

FIG. 8 depicts a schematic drawing of a scanning projector in accordancewith a second alternative embodiment of the present invention.

FIG. 9 depicts operations of a method for enhancing the visibility ofsubcutaneous vein structure in accordance with the second alternativeembodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 depicts a schematic drawing of a scanning laser projector inaccordance with the prior art. Projector 100 comprises light sources102-1 through 102-3, beam combiner 106, scanner 108, and processor 126.Examples of conventional scanning laser projectors can be found in, forexample, U.S. Pat. No. 7,978,189, issued Jul. 12, 2011, which isincorporated herein by reference.

Light sources 102-1 through 102-3 are laser diodes that provide narrowspectral-width light signals 104-1 through 104-3, respectively (referredto, collectively, as light signals 104). Light source 102-1 provideslight signal 104-1, which is a light signal of a wavelength in the bluelight region (e.g., 445 nm). Light source 102-2 provides light signal104-2, which is a light signal of a wavelength in the green light region(e.g., 532 nm). Light source 102-3 provides light signal 104-3, which isa light signal of a wavelength in the red light region (e.g., 640 nm).Each of light sources 102-1 through 102-3 includes beam-shaping optic110 that shapes each of light signals 104-1 through 104-3 intosubstantially collimated beams and directs them along axes 112-1, 112-2,and 112-3, respectively.

Beam combiner 106 comprises selective fold mirrors 114-1 and 114-2.Selective fold mirror 114-1 is a dichroic mirror that is transparent forlight signal 104-1 but substantially reflects light signal 104-2.Selective fold mirror 114-1 is aligned at an angle of 45° with respectto each of axes 110-1 and 110-2.

Selective fold mirror 114-2 is a dichroic mirror that is transparent forlight signals 104-1 and 104-2 but reflects light signal 104-3. Selectivefold mirror 114-2 is aligned at an angle of 45° with respect to each ofaxes 110-1 and 110-3. Typically, light sources 102, beam-shaping optics110, and mirrors 114-1 and 110-2 are mounted in a rigid fixture, such asan optical sub-mount, which keeps them in their relative positions.

In operation, beam combiner 106 receives each of light signals 104-1 and104-2 such that the light signals are coincident at the center ofselective fold mirror 114-1. Selective fold mirror 114-1 allows lightsignal 104-1 to pass through and continue along axis 110-1 but turnslight signal 104-2 from axis 110-2 to axis 110, where it combines withlight signal 104-1 to form dual-wavelength light signal 116.

In similar fashion, beam combiner 106 receives light signal 104-3 suchthat it is coincident with light signal 116 at the center of selectivefold mirror 114-2. Selective fold mirror 114-2 allows light signal 116to pass through and continue along axis 110-1 but turns light signal104-3 from axis 110-3 to optical axis 110-1, where it combines withlight signal 116 to collectively define composite output signal 118.Composite output signal 118 exits beam combiner 106 as a collimatedfree-space beam 120.

Scanner 108 receives beam 120 and steers it about a two-dimensional coneto render an image on image region 122 of surface 124. Scanner 108 is aconventional scanner, such as a two-axis gimbal-mounted MEMS mirror, agalvo scanner, and the like. Processor 126 controls the angular positionof scanner 108 and, therefore, the position of beam 120 in image region122.

Processor 126 is typically a conventional digital video processorsuitable for interfacing with a video source (e.g., cell phone, PDA,etc.), modulating light sources 102-1 through 102-3 to control therelative intensities of light signals 104-1 through 104-3, andcontrolling scanner 108 so that it traces beam 120 appropriately acrossimage region 122.

Processor 126 normally comprises a video controller that receives aninput video signal from the video source and buffers the received videoimages in memory. To display a video frame, the controller reads the astored video frame from the memory and drives light sources 102 so thatthey emit their respective light signals at the appropriate intensityfor generating the desired color and brightness at each image pixel 128as beam 120 is scanned across image region 122.

Projectors based on free-space beam combiners, such as beam combiner106, are beset by several drawbacks, however. First, free-space beamcombiners require optical elements that are relatively large and bulky,which results in a projector that is also relatively large and bulky.Typically, scanning laser projectors are intended for use with that isroughly pocketsize. A reliance on free-space beam combiners has resultedin conventional laser projectors that are much larger than the videosources, however. As a result, the relatively large size of conventionalscanning projectors has, thus far, limited their widespread adoption.

Second, free-space beam combiners convey light through a medium (e.g.,air, glass, etc.) that provides no light-guiding capability. As aresult, it is necessary to include beam-shaping optics, such as acollimator, for shaping each constituent light signal prior to itsreceipt by the beam combiner to ensure that each beam has substantiallythe same cross-sectional shape when combined. The need for beam-shapingoptics adds significant system cost and complexity.

Third, the assembly of the optical elements of a free-space beamcombiner is typically highly labor intensive. These optical elementsmust be carefully aligned in both position and angle to ensure that theconstituent light signals are completely overlapping to avoid spectralnon-uniformity through the cross-section of the composite output beam.In addition, angular misalignment of one or more of constituent lightsignals can lead to divergence of those light signals as they propagatethrough the beam combiner. The assembly of these optical elementsbecomes increasingly more difficult as additional light signals areincluded. Further, high-speed volume manufacture of free-space beamcombiners is difficult in a cost-effective manner. Still further, thesources, mirrors, and lenses are normally aligned and positioned bymounting them in an optical fixture. Unfortunately, such fixtures aresusceptible to temperature-induced misalignments (due to thermalexpansion), as well as misalignments caused by shock and vibration thatcommonly occur through the lifetime of the projector.

Fourth, geometric distortion of the constituent light signals (e.g.,light signals 102-2 and 102-3) occurs at each turning mirror due to thedifference in the angle of incidence in the x- and y-directions betweenthe beams and the mirrors (e.g., mirrors 114-1 and 114-2). As a result,it is often necessary to include beam-shape compensation optics, whichfurther increases cost, complexity, and system size.

Fifth, conventional laser projectors rely on direct modulation of thelaser sources to control the color of the composite output signal.Unfortunately, changing the drive current to a laser diode can lead todeleterious optical effects, such as wavelength chirping and modehopping, that manifest as unwanted visible artifacts in the projectedimage. In addition, some laser sources, such as frequency-doubled lasersor diode-pumped solid-state lasers, cannot be controlled using directcurrent drive modulation and, therefore, rely upon external modulators,such as acousto-optic modulators, to control their output. Externalmodulation adds significant complexity and expense to such systems.

In contrast to projectors of the prior art, laser projectors inaccordance with the present invention employ beam combiners based onplanar lightwave circuits (PLCs). For the purposes of thisSpecification, including the appended claims, a “planar lightwavecircuit” is defined as an optical circuit that comprises one or moremonolithically integrated surface waveguide structures that guide lightin two dimensions, wherein the surface waveguides are arranged toprovide at least one optical function. Beam combiners in accordance withthe present invention comprise “high-contrast” surface waveguides whosecores comprise silicon nitride. Further, beam combiners in accordancewith the present invention enable a single composite light signal to beformed by combining light signals of disparate, irregularly spacedwavelengths over a wide wavelength range.

It should be noted that PLC-based devices exist in the prior art thatcan be used to combine two or more light signals of differentwavelengths—namely, array waveguide gratings (AWGs). An AWG, however,requires that the wavelengths being combined be closely spaced and beregularly spaced. As a result, an AWG does not have the diversity andflexibility required for laser projector applications.

FIG. 2 depicts a schematic drawing of a scanning projector in accordancewith an illustrative embodiment of the present invention. Projector 200comprises light sources 202-1 through 202-3, beam combiner 206, lens220, scanner 108, and processor 126. Projector 200 projects a full-colorimage in the visible light range.

FIG. 3 depicts operations of a method for projecting an image inaccordance with the illustrative embodiment of the present invention.Method 300 begins with operation 301, wherein light signals 204-1through 204-3 (referred to, collectively, as light signals 204) aregenerated by light sources 202-1 through 202-3 (referred to,collectively, as light sources 202). Method 300 is described withcontinuing reference to FIG. 2 and reference to FIGS. 4-7.

Light sources 202-1 through 202-3 are laser diodes that provide narrowspectral-width light signals 204-1 through 204-3, respectively (referredto, collectively, as light signals 204). Light source 202-1 provideslight signal 204-1, which is a light signal of a wavelength in the blueregion (e.g., 445 nm). Light source 202-2 provides light signal 204-2,which is a light signal of a wavelength in the green light region (e.g.,532 nm). Light source 202-3 provides light signal 204-3, which is alight signal of a wavelength in the red light region (e.g., 640 nm). Insome embodiments, light signals 204 are characterized by differentwavelengths within the visible light region. In some embodiments, atleast one of light signals 204 is characterized by a wavelength that isoutside of the visible light region, such as the ultraviolet region,near-infrared region, or mid-infrared region.

At operation 302, light signals 204 are combined at beam combiner 206 toform composite output signal 218.

Beam combiner 206 is a PLC-based beam combiner that comprises waveguides208-1 through 208-3, input ports 210-1 through 210-3, power controllers212-1 through 212-3, mixing region 214, and output port 216.

Each of waveguides 208-1 through 208-3 (referred to, collectively, aswaveguides 208) is a single-mode waveguide characterized by a largedifference between the refractive index of its core material andcladding material (typically referred to as “a high-contrastwaveguide”). As a result, each of waveguides 208 is characterized bystrong optical mode confinement, can include curved sections that havesmall bend radii, and can include waveguides in a densely packedarrangement. Planar lightwave circuits based on waveguide 208,therefore, can provide a high degree of functionality in a much smallerfootprint than conventional low-index waveguide-based planar lightwavecircuits.

FIG. 4A depicts a schematic drawing of a cross-sectional view of awaveguide in accordance with the illustrative embodiment of the presentinvention. Waveguide 208 is a composite-core waveguide (referred to,herein, as a TriPleX™ waveguide), such as is described in U.S. Pat. No.7,146,087, issued Dec. 5, 2006, which is incorporated herein byreference. Waveguide 208 comprises lower cladding 402, core 404, andupper cladding 406. Waveguide 208 is representative of each ofwaveguides 208-1 through 208-3.

Waveguide 208 is based on a material system of silicon nitride andsilicon dioxide. Such a waveguide can be designed for operation at anywavelength from the ultraviolet range to the mid-infrared range. As aresult, beam combiner 206 enables projector 200 to project light beamsof a diversity of irregularly or regularly spaced wavelengths. Oneskilled in the art will recognize that conventional silica-based PLCtechnology is not well suited to applications wherein multiple lightsignals characterized by disparate wavelengths over a wide wavelengthrange must be combined.

Lower cladding 402 is a layer of silicon dioxide having a thicknesstypically within the range of approximately 1 micron to approximately 10microns. Lower cladding 402 can be formed by any of a number ofconventional methods, including thermal growth, LPCVD deposition,spin-on coating, and the like. It will be clear to one skilled in theart how to specify, make, and use lower cladding 402.

Core 404 comprises inner core 408 and outer core 410, which completelysurrounds inner core 408.

Inner core 408 comprises stoichiometric silicon dioxide. Inner core 408has a substantially square cross-sectional shape having a size, w1, ofapproximately 1 micron on a side. In some embodiments, inner core 408has a different shape and/or different dimensions.

Outer core 410 comprises stoichiometric silicon nitride having athickness equal to w2. In the illustrative embodiment, w2 isapproximately equal to 200 nm; however, it will be clear to one skilledin the art, after reading this Specification, how to specify, make, anduse alternative embodiments of the present invention wherein w2 is anypractical size.

In some embodiments, outer core 410 does not completely surround innercore 410. In some embodiments, outer core 410 comprises a layer ofstoichiometric silicon nitride disposed on inner core 408 and/or a layerof stoichiometric silicon nitride that interposes inner core 408 andlower cladding 402.

Upper cladding 406 is a layer of silicon dioxide formed as a conformalcoating over core 404. Upper cladding 406 is formed using conventionalconformal deposition techniques, such as plasma-enhanced chemical vapordeposition, low-pressure chemical vapor deposition using tetraethylorthosilicate (TEOS) as a precursor gas, and the like.

FIG. 4B depicts a schematic drawing of a cross-sectional view of awaveguide in accordance with a first alternative embodiment of thepresent invention. Waveguide 412 is a silicon-nitride-core waveguidethat comprises lower cladding 402, core 414, upper cladding 406, andbarrier layer 420.

Core 414 comprises lower core 416 and upper core 418, which is disposedon lower core 416.

Lower core 416 comprises stoichiometric silicon nitride. Lower core 416has a substantially rectangular cross-sectional shape having a widthwithin the range of approximately 0.8 microns to approximately 3 micronsand a height within the range of approximately 3 nm to approximately 30nm. In some embodiments, lower core 416 has a different shape and/ordifferent dimensions.

Upper core 418 comprises silicon dioxide deposited using TEOS as aprecursor gas. Upper core 418 has a width substantially equal to thewidth of lower core 416 and a thickness within the range ofapproximately three to approximately twenty times the thickness of lowercore 416. In some embodiments, upper core 418 enables a reduction in theinternal stress of lower core 416 and/or reduces scattering in lowercore 416, as well as having other positive effects that lead to areduction in propagation loss for light propagating through waveguide412. One skilled in the art will recognize, after reading thisSpecification, that the dimensions of lower core 416 and/or upper core418 are based on several factors, including the wavelength of light thatis expected to propagate through the waveguide.

Upper cladding 406 is covered with optional barrier layer 420. Barrierlayer 420 comprises silicon nitride and provides a barrier to moistureand contaminants that might otherwise be absorbed by waveguide 412. Insome embodiments, barrier layer 420 is not included.

One skilled in the art will recognize, after reading this Specification,that the waveguide structures depicted in FIGS. 4A and 4B represent onlytwo examples of waveguide structures suitable for use in beam combiner206. It will be clear to one skilled in the art, after reading thisSpecification, that waveguide structures suitable for use in beamcombiner 206 include, without limitation, ridge waveguides, channelwaveguides, stripe waveguides, multi-layered waveguides, femto-secondlaser-written waveguides, graded-index waveguides, and the like.

At its input, each of waveguides 208 comprises an input port thatcomprises a mode-matching region, which enables the waveguide tooptically couple light directly from the output facet of itscorresponding light source 202 without large coupling losses.Specifically, waveguide 208-1 comprises input port 210-1, which enableslow-loss optical coupling with light source 202-1, waveguide 208-2comprises input port 210-2, which enables low-loss optical coupling withlight source 202-2, and waveguide 208-3 comprises input port 210-3,which enables low-loss optical coupling with light source 202-3.

FIG. 5A depicts a schematic drawing of a top view of an input portcomprising a mode-matching region in accordance with the illustrativeembodiment of the present invention. Input port 210-i is representativeof each of input ports 210-1 through 210-3.

Mode-matching region 502-i is a region of waveguide 208-i whosecross-sectional area is gently tapered such that it increasesmonotonically from end facet 504-i to interface 506-i along length L.Mode-matching region 402-i, therefore, gently transitions from (1) aneffective index-contrast that yields a mode-field diameter at end facet504-i that substantially matches the mode-field diameter of the lightsource to (2) an effective index-contrast that yields a mode-fielddiameter at interface 506-i that substantially matches the mode-fielddiameter of waveguide 208-i. As a result, the optical mode of lightpropagating through mode-matching region 402-i is matched to the opticalmode of the output facet of light source 202-i at end facet 504-i, whilethe optical mode of light propagating through mode-matching region 402-iis matched to the optical mode of waveguide 208-i at interface 506-i.

FIG. 5B depicts a schematic drawing of a cross-sectional view of endfacet 504-i. End facet 504-i comprises lower cladding 402, inner core510, outer core 512, and upper cladding 406.

Inner core 510 is analogous to inner core 408; however, inner core 510has a substantially square cross-sectional shape having a size of w1,where w1 is smaller than the size of inner core 408 (1 micron in theillustrative embodiment).

Outer core 512 is analogous to outer core 410; however, outer core 512has a thickness of w2, where w2 is smaller than the thickness of outercore 410 (200 nm in the illustrative embodiment).

FIG. 5C depicts a schematic drawing of a cross-sectional view ofinterface 506-i. Interface 506-i comprises lower cladding 402, innercore 408, outer core 410, and upper cladding 406. In other words,interface 506-i has the same dimensions and layer structure as waveguide208. As a result, light propagating through mode-matching region 503-iexperiences substantially lossless (i.e., adiabatic) transition intowaveguide 208.

It should be noted that, in some embodiments, the inclusion ofmode-matching regions in the input ports of a beam combiner mitigatesmany of the assembly issues that impact prior-art projectors by enablinglight sources 202 to be easily integrated with beam combiner 206 bymounting the laser diodes directly on the beam combiner substrateitself. This enables each light signal output at the output facets ofthe laser diodes to be directly coupled into its corresponding inputport 210. As a result, the integrated light sources and beam combinercollectively define a substantially solid “light engine” that is morerobust and can be significantly more compact than possible withprior-art approaches.

In some embodiments, however, light sources 202 are not directlyintegrated with beam combiner 206. In some embodiments, light sources202 are fiber-coupled laser diodes that provide light signals 204 tobeam combiner 206 via optical fiber pigtails that are attached directlyto appropriately mode-matched input ports of a beam combiner.

One skilled in the art will recognize, after reading this specification,that since waveguides 208 provide waveguiding in two dimensions, lightsignals 204 need not be collimated prior to their coupling into the beamcombiner. This eliminates the need for beam-shaping optics at each lightsource. It also mitigates the effects of angular misalignment, sincespectral non-uniformity through the cross-section of the compositeoutput beam and beam divergence issues are eliminated. Further, theelimination of the beam-shaping optics and the integration of the lightsources and beam combiner enable a significant reduction in the overallsize of the optical system. In fact, in some embodiments, the size ofthe optical system is small enough to enable a pen-sized projector 200,or enable projector 200 to be integrated directly into a mobile digitaldevice, such as a cell phone or personal digital assistant (PDA).

FIG. 6 depicts a schematic drawing of mixing region 214. Mixing region214 comprises portions of waveguides 208-1 through 208-3, which havebeen arranged to form directional couplers 602-1 and 602-2.

Directional coupler 602-1 comprises first portions of waveguides 208-1and 208-2, which are separated by gap g1 along interaction length L1.Directional coupler 602-1 is a symmetric coupler (i.e., the portions ofwaveguides 208-1 and 208-2 have substantially the same width) that ischaracterized by wavelength-dependent power coupling that varies slowlywith wavelength. The values of g1 and L1 are carefully chosen to enablesubstantially all of the optical energy in light signal 204-1 tooptically couple from waveguide 208-1 into waveguide 208-2 alonginteraction length L1, but substantially none of the optical energy inlight signal 204-2 optically couples from waveguide 208-2 to waveguide208-1. As a result, directional coupler 602-1 provides both lightsignals 204-1 and 204-2, combined as dual-wavelength signal 604, onwaveguide 208-2.

Directional coupler 602-2 comprises a second portion of waveguide 208-2and a portion of 208-3, which are separated by gap g2 along interactionlength L2. Directional coupler 602-2 is also a symmetric coupler that ischaracterized by wavelength-dependent power coupling that varies slowlywith wavelength. The values of g2 and L2 are carefully chosen to enablesubstantially all of the optical energy in light signal 204-3 tooptically couple from waveguide 208-3 into waveguide 208-2 alonginteraction length L2, but substantially none of the optical energy inlight signal 604 optically couples from waveguide 208-2 to waveguide208-3. As a result, directional coupler 602-2 provides all three oflight signals 204-1 through 204-3, combined as composite output signal218, on waveguide 208-2.

Although the illustrative embodiment comprises a beam combiner havingthree waveguides and three input ports, it will be clear to one skilledin the art, after reading this Specification, how to specify, make, anduse alternative embodiments that comprise beam combiners having anypractical number of waveguides and input ports. As discussed in U.S.patent application Ser. No. 13/208,806, beam combiners in accordancewith the present invention can include additional branches or hierarchystages that enable the addition of additional light signals to thesystem. The ability to readily include more waveguides and portsenables, for example, the inclusion of redundant light sources for eachlight signal without significantly increasing the overall size ofprojector 200.

At operation 303, processor 126 controls the ratio of optical power fromlight signals 204 in composite output signal 218 via power controllers212-1 through 212-3.

FIG. 7 depicts a schematic drawing of a power controller in accordancewith the illustrative embodiment of the present invention. Controller212-i comprises attenuator 702-i and power monitor 704-i. In response tocontrol signals from processor 126 (not shown for clarity) and theoutput of power monitor 704-i, controller 212-i diverts optical power(via attenuator 702-i) from waveguide 208-i to a light dump in order tocontrol the amount of optical power of light signal 204-i that reachesmixing region 214.

Attenuator 702-i comprises waveguide 208-i and waveguide 708-i, whichare arranged to define directional couplers 708-1 and 708-2.

Directional couplers 708-1 and 708-2 are substantially identicaldirectional couplers arranged in series and interposed by waveguideportions 710-i and 712-i. Waveguide portion 710-i is a first portion ofwaveguide 208-i. Waveguide portion 712-i is a waveguide having structureanalogous to that of waveguide 208. Waveguide portion 712-i is opticallycoupled with light dump 716-i. It will be clear to one skilled in theart how to specify, make, and use light dump 716-i.

Modulator 714-i comprises a heater strip for thermally inducing a phaseshift in the light that propagates through waveguide portion 710-i. Thisphase shift determines the amount of optical coupling occurs betweenwaveguide portions 710-i and 712-i. This optical coupling, in turn,dictates how much of the optical power of light signal 204-i is divertedinto waveguide portion 712-i and lost at light dump 716-i. The remainderof light signal 204-i continues propagating in waveguide 208-i to output724-i.

Although the illustrative embodiment comprises modulators that operateon a thermo-optic effect, it will be clear to one skilled in the art,after reading this Specification, how to specify, make, and usealternative embodiments of the present invention that comprisemodulators that induce a phase shift in light propagating in a waveguidebased on a different effect, such as electro-optic, opto-mechanical,etc.

Power monitor 704-i comprises waveguide 208-i, waveguide 718-i, andphotodetector 722-i. Waveguide 208-i and waveguide 718-i are arranged todefine directional coupler 720-i.

Directional coupler 720-i enables a small percentage of its opticalpower to be coupled from waveguide 208-i into waveguide portion 718-i.

Waveguide portion 718-i is optically coupled with conventionalphotodetector 722-i (e.g., photodiode, avalanche photodiode, CCD sensorelement, etc.), which is electrically coupled with controller 132 toprovide the controller with a feedback signal suitable for controllingattenuator 702-i.

It is an aspect of the present invention that the use of powercontrollers 212-1 through 212-3 obviates the need to vary the drivecurrent to each of light sources 202 to control the color of compositeoutput signal 218. As a result, embodiments of the present invention canavoid undesirable optical effects in the composite output signal, suchas wavelength chirping, accelerated degradation, mode hopping, and thelike. The use of power controllers 212 also enables the use of lasersources, such as frequency doubled lasers or diode-pumped solid-statelasers, without a need for their customary external modulators. Further,since the attenuators are easily integrated in the PLC design, theirinclusion adds little or no additional size to the overall system. Itshould be noted, however, that in some embodiments, power controllers212 are not included and the intensity of light signals 204 iscontrolled conventionally by controlling the drive current to each oflight sources 202.

At operation 304, composite output signal 218 is emitted into free spaceat output port 216. Composite output signal 218 is received by lens 220,which substantially collimates the signal to form output beam 222. Lens220 is a conventional bulk optic lens suitable for collimating theoptical emission at output port 216. In some embodiments, lens 220 is anintegrated lens formed directly on the exit facet of output port 216.

At operation 305, scanner 108 receives output beam 222 and scans it overregion 122 to form an image on sample 124.

It should be noted that projector 200 provides a collimated light beamthat remains in focus, even when projected onto a surface that is notflat. In addition, image resolution is determined only by the spot sizeof output beam 222, rather than the resolution of a CCD camera, videoprocessor, or liquid-crystal element, which enables a simpler, cheaperprojection system.

The advantages afforded embodiments of the present invention enable aprojector platform that is adaptable for use in many applications beyondthat of simple image projection. It should be noted, therefore, that theillustrative embodiment represents only one example of a projector inaccordance with the present invention. Alternative embodiments includeprojectors adapted for use in applications that include, withoutlimitation, visualization and treatment of cancer tissue, pest control,insect control, visual enhancement of hot spots in semiconductormaterial or integrated circuits, virtual keyboards, smart targetingsystems for laser-guided munitions, laser-based weapons, confocalmicroscopy, laser light based quality control in the medical or foodindustry or laser based sorting in waste and recycling processes, etc.As a result, details of the projector and the method for its use, suchas the number of light signals, wavelengths selected, componentarrangement, and the like, are for example only and one skilled in theart will recognize that embodiments of the present invention suited forsome or all of these applications will differ from the illustrativeembodiment described herein.

Vein Imaging

An application for which the present invention is particularly wellsuited for is the enhancement of the visibility of subcutaneous veinstructure in bodily tissue. Enhanced vein visibility facilitates theperformance of medical procedures by a medical practitioner, such asinsertion of catheters, syringes, intravenous tubes, identification ofblood clots or internal hemorrhaging, minimally invasive surgery, andthe like.

Vein imaging systems are known in the prior art, such as systemsdescribed in U.S. Patent Application Publication 2008/0004525, publishedJan. 3, 2008 and U.S. Patent Application Publication 2008/027317,published Jan. 31, 2008, each of which is incorporated herein byreference.

In U.S. Patent Application Publication 2008/0004525 (hereinafterreferred to as the “525 application”), a scanning projector scans afirst light signal over a image points in a sample region, wherein thefirst light signal of a wavelength that is readily absorbed by blood(i.e., 740 nm). The first light signal is reflected from the imagepoints and detected at a photodetector. The output of the photodetectoris used to create a digital map of the absorption of the first lightsignal in the sample region, wherein the absorption map represents thevein structure within the scanned area. Once this absorption map hasbeen created, it is projected, using the same projection system, overthe sample region using a second light signal of a wavelength visible tothe eye (e.g., 630 nm).

Unfortunately, the system disclosed in the 525 application has severaldrawbacks. First, the absorption map is generated over the entire sampleregion (during a period of 60 frames of the video cycle) prior torendering the visible image of the vein structure (also during a periodof 60 frames of the video cycle). This leads to a significant delaybetween the projection of each successive visible image on the sample.As a result, this system is prone to errors due to practitioner handjitter or patient motion. In addition the system is also prone to thedevelopment of image flicker, which, in addition to creating anannoyance, can also lead to more serious issues such as epilepticseizure.

In addition, the system disclosed in the 525 application employs afree-space beam combiner into which the outputs of the 740 nm and 630 nmlasers are “projected.” Further, the 740 nm and 630 nm lasers aredirectly driven to control their output. As a result, this system ischaracterized by most, if not all, of the same disadvantages asprojector 100, described above and with respect to FIG. 1.

In U.S. Patent Application Publication 2008/027317 (hereinafter referredto as the “317 application”), a scanning projector scans a first lightsignal over a image points in a sample region, wherein the first lightsignal is also characterized by a wavelength that is long enough to beabsorbed by blood (e.g., 740 nm). The first light signal is reflectedfrom the image points and detected at a photodetector that isselectively sensitive to the wavelength of the first light signal. Whenthe output of the photodetector indicates the presence of a vein at animage point, a second light signal of a visible wavelength is added tothe first light signal. The two light signals are combined using afree-space optical system based on “dielectric mirrors.”

Unfortunately, the system disclosed in the 317 application also hasseveral drawbacks. First, in contrast to the present invention,free-space optics are used to combine the light signals. Second, thissystem also relies on direct modulation of the intensities of the lasersources. As a result, the system disclosed in the 317 application alsohas all the same disadvantages of projector 100, as described above andwith respect to FIG. 1.

In contrast to the prior art, however, embodiments of the presentinvention are suitable for enhancing the visibility of vein structurewithout some of the disadvantages inherent in projectors that rely onfree-space optics-based beam combiners and directly modulated lasersources.

FIG. 8 depicts a schematic drawing of a scanning projector in accordancewith a second alternative embodiment of the present invention. Projector800 is a projector for enhancing the visibility of the subcutaneous veinstructure of a region of bodily tissue. Projector 800 comprises lightsources 202-4 and 202-5, beam combiner 802, scanner 108, photodetector818, and processor 822.

Projector 800 is analogous to projector 200 in that it scans an outputbeam having multiple light signals over an image region. Projector 800,however, scans a beam including a first signal of a first wavelengthover the image region and controls the presence of a second light signalin the beam based a property of each image point in the image region.The property of each image point is determined based on reflected lightof the first light signal. As a result, projector 800 projects real-timedata about the image points in the image region, wherein projector 200projects only predetermined information (e.g., video frames, stillimages, etc.).

Specifically, projector 800 interrogates image points in the region witha light beam comprising a first light signal of a first wavelength,which is readily absorbed by blood. The projector monitors how much ofthe first light signal is reflected from each image point to determinethe presence of a vein at that image point. When a drop in the reflectedlight from an image point is detected (indicating the presence of avein), the projector adds a second light signal of a visible wavelengthto the light beam to illuminate that image point for the user. Byscanning the light beams over all of the image points in the region at asufficient rate, a real-time video image of the subcutaneous veinstructure is rendered directly on the sample region.

FIG. 9 depicts operations of a method for enhancing the visibility ofsubcutaneous vein structure in accordance with the second alternativeembodiment of the present invention. Method 900 begins with operation901, wherein light signal 204-4 is coupled into output beam 808.

Light signal 204-4 is provided to beam combiner 802 by light source202-4, which is a laser diode that emits narrow-spectral-width light ata wavelength of approximately 740 nm. In some embodiments, light signal204-4 is characterized by a different wavelength that is readilyabsorbed by blood (e.g., 850 nm, etc.). Light source 202-4 is mountedsuch that it is directly optically coupled with input port 210-4 of beamcombiner 802.

Beam combiner 802 is analogous to beam combiner 206, described above andwith respect to FIG. 2; however, beam combiner 802 is dimensioned andarranged to combine only two light signals into a composite output beam.Beam combiner 802 comprises input ports 210-4 and 210-5, attenuators702-4 and 702-5, mixing region 804, and output port 216.

Each of input ports 210-4 and 210-5 includes a mode-matching region forenabling direct, low-loss optical coupling of light signals 204-4 and204-5 from the output facets of light sources 202-4 and 202-4,respectively, to beam combiner 802. Input ports 210-4 and 210-5 areanalogous to input ports 210-i, described above and with respect toFIGS. 5A-C.

Light signal 204-4 is conveyed to mixing region 804 via attenuator702-4, which controls the intensity of light signal 204-4 in output beam808 as described above and with respect to FIG. 7.

Mixing region 804 is analogous to mixing region 206; however, sinceprojector 800 utilizes only two light signals, mixing region 804comprises only directional coupler 602-3. Directional coupler 602-3 isdimensioned and arranged to combine light signals 204-4 and 204-5 intocomposite output signal 806, as described above and with respect to FIG.6.

Beam combiner 802 provides composite output signal 806 at output port216, where it is collimated by lens 220 to form output beam 808.

At operation 902, scanner 108 directs output beam 808 to image point810-i-j, wherein i=1 to M, j=1 to N, M is the number of rows of imagepoints in region 812, and N is the number of columns of image points inregion 812.

At operation 903, photodetector 818 receives reflected signal 816 fromimage point 810-i-j. Reflected signal 816 is a portion of output beam808 that is reflected from the image point toward photodetector 818.

Photodetector 818 is a conventional photodetector that generateselectrical signal 820, whose instantaneous magnitude is based on theinstantaneous intensity of reflected signal 816. In some embodiments,photodetector 818 comprises a filter that enables photodetector 818 toselectively detect light of the wavelength of light signal 204-4. Insuch embodiments, the overall system signal-to-noise ratio is improvedsince background noise can be reduced significantly. In someembodiments, photodetector 818 comprises a filter that enablesphotodetector 818 to selectively detect light of a wavelength other thanthe wavelength of light signal 204-4. In some embodiments, photodetector818 comprises a filter that enables photodetector 818 to detect light ofonly one polarization.

At operation 904, processor 822 tests reflected signal 816 forabsorption of light signal 204-4 at image point 810-i-j. Due to thechoice of wavelength for light signal 204-4, the presence of a vein atimage point 810-i-j induces a detectable drop in the intensity ofreflected signal 816.

Processor 822 is a conventional processor suitable for executingcomputer programs, storing data, receiving electrical signal 820 fromphotodetector 818, and providing drive signals 824-4 and 824-5 to lightsources 204-4 and 204-5, control signals 826-4 and 826-5 to attenuators702-4 and 702-5, and drive signal 828 to scanner 108.

If absorption is detected at image point 810-i-j, method 200 continueswith operation 905, wherein light signal 204-5 is added to output beam808.

Light signal 204-5 is provided to beam combiner 802 by light source202-5, which is a laser diode that emits narrow-spectral-width greenlight having a wavelength of approximately 532 nm. In some embodiments,light signal 204-5 is characterized by a different wavelength in thevisible wavelength range. Although the human eye is most sensitive tolight within the green wavelength range (i.e., the range fromapproximately 520 nm to approximately 570 nm), one skilled in the artwill recognize that many other wavelengths of light are suitable for usein light signal 204-5, such as 633 nm, 650 nm, 670 nm, 593.5 nm, 473 nm,and 405 nm, among others. The addition of light signal 204-5 to outputbeam 808 while it is directed at image point 812-i-j enhances thevisibility of this image point for a user.

In some embodiments, light signal 204-5 is characterized by a wavelengththat is suitable for exciting a phosphor used in vision enhancementsystems (e.g., night vision goggles, etc.). Such embodiments aresuitable, for example, to enable medical procedures to be carried outwhen stealth is desired, such as on a battlefield, or in otherapplications wherein a medical practitioner might be wearing such visionenhancement equipment.

In some embodiments, at least one of light signals 204-4 and 204-5 ischaracterized by a wavelength suitable for exciting a fluorescentmaterial or phosphor, such as a fluorescent biomarker, that is locatedin or on the target sample.

The presence of light signal 204-5 in output beam 808 is controlled viacontrol signal 826-5 provided by processor 822 to modulator 714-5 ofattenuator 702-5. To add light signal 204-5 to output beam 808,modulator 714-5 is driven such that substantially all of the opticalenergy of light signal 204-5 remains in waveguide 208-5, as discussedabove and with respect to FIG. 7. To eliminate light signal 204-5 fromoutput beam 808, modulator 714-5 is driven such that substantially allof the optical energy of light signal 204-5 couples into waveguideportion 712-5 to be lost at light dump 716-5. In some embodiments, lightsignal 204-5 is added to output beam 808 by directly controlling drivesignal 824-5.

At operation 906, light signal 204-5 is removed from output beam 808.

At operation 907, scanner 108 indexes output beam 808 to the next imagepoint in the scanning pattern used to interrogate region 812. In someembodiments, scanner 108 raster scans output beam 808 over the imagepoints in region 812. In some embodiments, scanner 108 uses a non-rasterscanning pattern to interrogate the image points.

Returning to operation 905, if absorption is not detected at image point810-i-j during operation 205, method 900 skips operation 206 and movesdirectly to operation 907. As a result, image point 810-i-j is notilluminated by light signal 108.

Operations 902 through 907 are repeated for each i=1 to M and j=1 to Nsuch that projector 800 repeatedly scans the entirety of region 812 at arate that enables a visible image of the subcutaneous vein pattern inregion 812 to be rendered on surface 814.

One skilled in the art will recognize, after reading this Specification,that more than two light signals can be combined via beam combiners inaccordance with the present invention, to enable, for example,interrogation of region 812 with more than one wavelength of light. Insome embodiments, interrogating region 812 with a plurality ofwavelengths provides advantages that include: improved measurandselectivity, the ability to determine more than one measurand, andimproved measurement resolution, among others. In some embodiments, theuse of multiple wavelengths for interrogation enables detection ofspecific chemicals, nuclear material, explosive materials, surfacestructure in an image region, and/or sub-surface structure in an imageregion. Further, additional wavelengths can be included for enhancingthe projected image to render additional images of, for example, surfacestructure in the image region, sub-surface structure in the imageregion, graphics, text, and the like.

Vein-imaging systems in accordance with the present invention have manyadvantages over vein-imaging systems known in the prior art. Bydirecting a single, collimated light beam that both interrogates andilluminates a scan region, all optical power can be provided to a singleimage point at the same time and the light beam is always in focus. Inaddition, by using one high-sensitivity photodetector, the need tospread the reflected signal over a large array of detector pixels isobviated. As a result, the collector optics can be simpler and lessexpensive, no alignment is needed between the detector array and theprojection system, and a higher signal-to-noise ratio can be achieved.Further, since no detector array is included, no video processing isnecessary. This reduces cost and increases system speed.

High-Power Laser Projection

In some applications, such as laser-guided munitions, laser-weaponry,and the like, it is desirable to scan and/or track an object with anoutput beam that comprises a very high power laser beam. For example, insome cases, once a projector has identified the presence of a targetmaterial at an image point, a user might want to add a high-power lasersignal to the output beam to induce an effect at that image point, suchas: illuminating the image point with a targeting-laser signal to directa laser-guided munition; inducing combustion, or other chemical change,of material at the image point to burn the wings off an insect (e.g., amosquito, wasp, etc.), ablate cancerous tissue, or add an identifyingmark to the image point.

Conventional PLC-based systems, however, are unable to handle high-powerlight signals, due to the fact that they require doping with impuritiesto affect a refractive index difference between the core and cladding oftheir constituent waveguides.

In contrast to the prior art, waveguides in accordance with the presentinvention are not doped and, therefore, can handle higher power lasersignals. Beam combiners in accordance with the present invention arebased on waveguide structures exhibit guiding capability based on thedifference of the refractive indices of stoichiometric silicon nitrideand stoichiometric silicon dioxide. As a result, projectors comprisingPLC-based beam combiners in accordance with the present invention enablethe inclusion of high-power laser signals in their output beams.

It is to be understood that the disclosure teaches just one example ofthe illustrative embodiment and that many variations of the inventioncan easily be devised by those skilled in the art after reading thisdisclosure and that the scope of the present invention is to bedetermined by the following claims.

1. A scanning projector comprising: a first light source that provides afirst light signal characterized by a first wavelength; a second lightsource that provides a second light signal characterized by a secondwavelength; a beam combiner comprising a planar lightwave circuitincluding a plurality of waveguides that are arranged to define a firstinput port, a second input port, a mixing region, and an output port,the beam combiner: (1) receiving the first light signal at the firstinput port, (2) receiving the second light signal at the second inputport, (3) combining the first light signal and the second light signalinto a composite output signal, and (4) providing the composite outputsignal at the output port; and a scanner, the scanner receiving thecomposite output signal from the beam combiner and scanning thecomposite output signal over each of a plurality of image points in afirst region.
 2. The projector of claim 1 wherein the planar lightwavecircuit comprises a first waveguide having an inner core comprisingsilicon dioxide and an outer core comprising silicon nitride.
 3. Theprojector of claim 1 wherein the planar lightwave circuit comprises afirst waveguide having a core comprising silicon nitride.
 4. Theprojector of claim 1 wherein the planar lightwave circuit comprises afirst waveguide comprising: a first layer comprising silicon nitride;and a second layer comprising silicon dioxide, the second layer disposedon and in contact with the first layer, and the second layer being aTEOS-based layer.
 5. The projector of claim 1 further comprising aphotodetector, the photodetector being dimensioned and arranged toreceive a reflected light signal from each of the plurality of imagepoints and generate a first electrical signal based on a characteristicof the received light signal; and a processor that controls the secondlight source based on the first electrical signal.
 6. The projector ofclaim 5 wherein the characteristic is intensity.
 7. The projector ofclaim 5 wherein the characteristic is polarization mode.
 8. Theprojector of claim 5 wherein the characteristic is wavelength.
 9. Theprojector of claim 1 further comprising: a third light source thatprovides a third light signal characterized by a third wavelength; and athird input port, wherein the plurality of waveguides are arranged tofurther define the third input port, the beam combiner receiving thethird light signal at the third input port and combining the third lightsignal into the composite output signal.
 10. The projector of claim 9wherein the first wavelength, second wavelength, and third wavelengthare irregularly spaced.
 11. The projector of claim 1 wherein the mixingregion comprises a plurality of directional couplers that is arranged ina first arrangement comprising a tree structure.
 12. The projector ofclaim 1 wherein the first input port includes a mode-matching regioncomprising (1) a first facet that is substantially mode-matched to anoutput facet of the first light source and (2) an interface that isoptically coupled with a first waveguide of the plurality of waveguides,and wherein the input port is optically coupled with each of the firstlight source and the first waveguide.
 13. The projector of claim 1wherein the planar lightwave circuit further comprises a firstattenuator, the first attenuator being dimensioned and arranged tocontrol the optical power of the first light signal in the compositeoutput signal.
 14. A scanning projector comprising: a plurality of lightsources, wherein each of the plurality of light sources provides adifferent one of a plurality of light signals, each of the plurality oflight signals being characterized by a different wavelength, and whereinthe plurality of wavelengths are irregularly spaced; a beam combinercomprising a planar lightwave circuit that includes a plurality of inputports, a mixing region, and an output port, wherein each of theplurality of input ports receives a different one of the plurality oflight signals, and wherein the mixing region combines the plurality oflight signals into a composite output signal that is provided at theoutput port; and a scanner, the scanner receiving the composite outputsignal from the beam combiner and scanning the composite output signalover each of a plurality of image points in a first region.
 15. Theprojector of claim 14 wherein the mixing region comprises a plurality ofdirectional couplers that are arranged in a tree structure.
 16. Theprojector of claim 14 wherein the planar lightwave circuit comprises afirst waveguide having a core comprising stoichiometric silicon nitrideand a cladding layer comprising silicon dioxide.
 17. The projector ofclaim 16 wherein the plurality of input ports comprises a first inputport that includes (1) an end facet that is optically coupled with afirst light source of the plurality of light sources and (2) aninterface that is optically coupled with the first waveguide, andwherein the end facet is characterized by a first optical mode thatsubstantially matches the output optical mode of the first light source,and further wherein the interface is characterized by a second opticalmode that substantially matches the optical mode of the first waveguide.18. The projector of claim 14 further comprising a photodetector, thephotodetector being dimensioned and arranged to receive a reflectedlight signal from each of the plurality of image points and generate afirst electrical signal based on a characteristic of the received lightsignal; and a processor that controls the second light source based onthe first electrical signal.
 19. The projector of claim 18 wherein thecharacteristic is intensity.
 20. The projector of claim 18 wherein thecharacteristic is polarization mode.
 21. The projector of claim 18wherein the characteristic is wavelength.
 22. The projector of claim 14wherein the planar lightwave circuit further comprises a firstattenuator, the first attenuator being dimensioned and arranged tocontrol the optical power of a first light signal of the plurality oflight signals in the composite output signal.
 23. A method comprising:receiving a first light signal characterized by a first wavelength at afirst input port of a beam combiner, wherein the beam combiner comprisesa planar lightwave circuit that includes the first input port and asecond input port, a mixing region, and an output port; receiving asecond light signal characterized by a second wavelength at the secondinput port; combining the first light signal and the second light signalin a composite output signal that is provided at the output port; andscanning the composite output signal over a first region.
 24. The methodof claim 23 further comprising providing the beam combiner such that thefirst input port includes a mode-matching region, the mode-matchingregion having (1) an end facet characterized by a first optical modethat substantially matches the output optical mode at an output facet ofa first light source that provides the first light signal and (2) aninterface characterized by a second optical mode that substantiallymatches the optical mode of a first waveguide, the planar lightwavecircuit comprising the first waveguide.
 25. The method of claim 23further comprising: providing the beam combiner such that the planarlightwave circuit includes an attenuator; and controlling the attenuatorto control the output power of the first light signal in the compositeoutput signal.
 26. The method of claim 23 further comprising: directingthe composite output signal at a first image point in the first region;generating a first electrical signal that is based on a first reflectedlight signal reflected from the first image point, wherein a firstcharacteristic of the first reflected light signal is based on a firstproperty of the first image point; and controlling the second lightsignal based on the first characteristic.
 27. The method of claim 26wherein the second light signal is controlled such that the second lightsignal has a first magnitude when the first characteristic has a firstvalue and a second magnitude when the first characteristic has a secondvalue that is different than the first value.
 28. The method of claim 26further comprising: directing the composite output signal at a secondimage point in the first region; generating a second electrical signalthat is based on a second reflected light signal reflected from thesecond image point, wherein a second characteristic of the secondreflected light signal is based on a second property of the second imagepoint; and controlling the second light signal based on the secondcharacteristic.